1. Field
Embodiments of the present disclosure generally relate to a wafer support cylinder used in a thermal process chamber.
2. Description of the Related Art
In many semiconductor device manufacturing processes, the required high levels of device performance, yield, and process repeatability can only be achieved if the temperature of the substrate (e.g., a semiconductor wafer) is tightly monitored and controlled during processing of the substrate. Rapid thermal processing (RTP), for example, is used for several different fabrication processes, including rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidation (RTO), and rapid thermal nitridation (RTN).
In a RTP chamber, for example, the substrate may be supported on its periphery by an edge of a substrate support ring that extends inwardly from the chamber wall and surrounds a periphery of the substrate. The substrate support ring is rested on a rotatable tubular support cylinder which rotates the substrate support ring and the supported substrate to maximize substrate temperature uniformity during processing. The support cylinder is made of opaque quartz to provide light shielding properties and low thermal conductivity such that heat from the processing area and/or the heating source is substantially attenuated near the support cylinder. The support cylinder is typically coated with a polysilicon layer to render it opaque to radiation in the frequency range used for temperature measurements of the substrate.
However, it has been observed that mismatch in thermal expansion coefficients of polysilicon layer and opaque quartz under high temperatures can cause cracking in the polysilicon layer and/or in the vicinity of the interface between the polysilicon layer and the opaque quartz. Such cracking can be detrimental to the substrate because the cracks may propagate into the underlying quartz which makes the polysilicon layer and a portion of the underlying quartz adhered to the polysilicon layer to peel after thermal cycling. The peeling of the polysilicon layer and the quartz pieces not only compromises opacity of the support cylinder but also contaminates the process chamber and the substrate with particles.
Therefore, there is a need for an improved support cylinder with enhanced light shielding properties that prevents contamination of the process chamber and the substrate during thermal processing.